The overall objective is to understand the mechanism of certain aspects of cell-mediated immunity, especially those pertaining to the interaction of sensitized lymphocytes and antigen leading to macrophage activation. This process appears to be important in immunity to microorganisms and tumors and may also underlie certain pathogenetic states. In this application, we propose to continue and extend ongoing work on lymphocyte mediators and their relation to macrophage activation using a mouse model. Specifically: 1) further biologic and physicochemical characterization of murine MIF; 2) studies to determine which cell type of subtype produces MIF; 3) studies on macrophage activation by lymphocyte mediators and comparison with in vivo activated macrophages; and 4) characterization and comparative function of murine MIF produced in vivo, a collaborative study.